A spool valve suitable for a hydraulic brake apparatus of a vehicle is disclosed in, for example, the below listed Patent Document 1. The disclosed spool valve includes a valve element (spool) and a cylinder (sleeve) which has a bore for accommodating the valve element to be movable in the axial direction. This spool valve is configured such that when the valve element in an initial position moves in the axial direction in relation to the cylinder, a supply valve port formed between the valve element and the cylinder opens, whereby working fluid is introduced from a hydraulic pressure source into a hydraulic chamber through the supply valve port.